A 4 cylinder, 2.0 liter engine Manufacted buy toyota found in mr2s, Celicas, and a few JDM only cars. There were 3 major generations to this engine. The first generation produced only 180hp, the sencond generation produced 225hp and the newest 3rd gen (found in celica st205s and mr2 sw20s) produced up to 255 hp. Some 4th generation engines that are sometimes defined as a 3rd/4th mix create up to 265 hp, making this engine one of the most powerful stock engines in a hp:displacement ratio. Tuners have consistantly produced over 400hp with engine upgrades. Some 3sgte have been known produce over 800 hp (this is a 2 liter engine folks!) like the one found in an mkiv supra.
3s refers to the block style and size. GTE refers to a GE (performance head) that is turbocharged. The 3sgte come stock with a ct26 turbo charger or a ct20b in the 3rd generation.